Fix combining AI and LOD Bias texture sampling coordinates

This change is to avoid incorrect constant folding results for negative values of AI (array index) coordinates. FPTOUI may produce poison values for such values.

Author: krystian-andrzejewski

IGC/Compiler/CISACodeGen/helper.cpp

@@ -2720,7 +2720,10 @@ namespace IGC
         Function* rdneFunc = GenISAIntrinsic::getDeclaration(
             builder.GetInsertBlock()->getModule(),
             GenISAIntrinsic::GenISA_ROUNDNE);
-        Value* intParam1 = builder.CreateFPToUI(
+        // FPToUI cannot be used to avoid generation of a poison value in case of
+        // the negative constant value. Such an approach is possible since
+        // there is a protection against exceeding limits by param1.
+        Value* intParam1 = builder.CreateFPToSI(
             builder.CreateCall(rdneFunc, param1),
             builder.getInt32Ty(),
             VALUE_NAME(std::string("_int") + param1Name));